As measurement of water quality or flowage in a marine area in the range of several km to several tens of km, on-site direct measurement, e.g., shipboard measurement or measurement at anchorage points predominates. However, such direct measurement requires a tremendous cost in terms of manpower or expenses in order to simultaneously measure various kinds of data covering a widespread marine area. Therefore, it is difficult to obtain surface data from a target of a marine area in the range of several km to several tens of km.
As a method of obtaining surface data based on simultaneous measurement from a target of marine area in the range of several km to several tens of km, there is a method using a marine radar. Further, as a conventional method of measuring a flow velocity distribution as marine surface data by using a marine radar, there is a method of processing reflected waves obtained by emitting electric waves to a sea surface as a video signal, generating a high-resolution radar image from this video signal, and calculating a flow velocity distribution based on this high-resolution radar image (Patent Literature 1).